Synergistic biocide composition containing pyrithione plus an additive

ABSTRACT

Disclosed herein is an antimicrobial composition characterized by synergistic antibacterial and antifungal efficacy and comprising a pyrithione salt or pyrithione acid, and at least one compound selected from the group consisting of benzyl and lower alkyl esters of para-hydroxybenzoic acid, salts thereof, carboxylic acids, salts thereof, and combinations thereof. Also disclosed is a method of imparting antimicrobial activity to a composition comprising water or an organic solvent which comprises adding thereto an antimicrobially effective amount of the above-described antimicrobial composition.

FIELD OF THE INVENTION

This invention relates generally to synergistic biocide compositions,and, more specifically, to a composition comprising pyrithione or apyrithione salt, and a benzyl or lower alkyl ester ofpara-hydroxybenzoic acid or a salt thereof, or a carboxylic acid or asalt thereof, or combination thereof.

BACKGROUND OF THE INVENTION

Biocides provide antimicrobial protection for industrial, personal care,medical and other products and materials. Typically, the biocide has asomewhat limited range with respect to the specific microorganisms itwill kill, has some toxicity, and presents some environmental hazard, ora combination of these drawbacks. Thus, it would be useful to find ameans to enhance biocidal activity, or extend the range of antimicrobialeffectiveness of biocides, without increasing toxicity or the degree ofenvironmental hazard of these compounds.

Certain combinations of pyrithione with other additives to provide apreservative, antibacterial or antifungal efficacy are known in the art.For example, Japanese Kokai 59-(1984)98001 discloses a cut flowerpreservative comprising pyrithione or a salt thereof, an aliphaticcarboxylic acid, and a saccharide. U.S. Pat. No. 4,242,336 discloses anantibacterial and antifungal composition comprising (a) at least onemember selected from the group consisting of dehydroacetic acid, sorbicacid and their alkali metal salts and (B) at least one member selectedfrom the group consisting of alkyl(aminoethyl)-glycines having C8 to C16alkyl groups and their salts, 2-pyridine-thiol 1-oxide (i.e.,pyrithione) and its salts, andtetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione. However, thesereferences do not disclose the basis for the efficacy of these disclosedcombinations, nor do they suggest other antimicrobial combinations.Furthermore, the sorbic acid disclosed in the '336 patent is subject tochemical instability problems, necessitating the use of a stabilizer toinhibit oxidation, such as manganous ion, as disclosed in U.S. Pat. No.5,354,902.

New combinations of pyrithione with other additives, exhibitingsynergistic efficacy over a wide range of use concentrations, withoutthe need for (and preferably in the absence of) any oxidative inhibitionstabilizer, would be highly desired by the biocides community,particularly if such compositions also exhibit low toxicity againstmammals. The present invention provides several of such combinations.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to an antimicrobialcomposition characterized by synergistic antibacterial and antifungalefficacy and comprising pyrithione acid or a pyrithione salt, or acombination thereof, and at least one compound selected from the groupconsisting of benzyl and lower alkyl esters of para-hydroxybenzoic acid,salts thereof, carboxylic acids, salts thereof, and combinationsthereof, said carboxylic acid being selected from the group consistingof gallic, malic, tartaric, undecylenic, salicylic, p-aminobenzoic,benzoic, propionic, lactic, citric acids and combinations thereof. Theantimicrobial composition is preferably free of an oxidative inhibitionstabilizer additive.

In another aspect, the present invention relates to a method ofimparting antimicrobial activity to a composition comprising water or anorganic solvent which comprises adding thereto an antimicrobiallyeffective amount of the above-described antimicrobial composition.

In yet another aspect, the present invention relates to a method ofcoating a substrate to provide an antimicrobially effective coating onthe substrate which comprises contacting the substrate with a coatingcomposition comprising the above-described antimicrobial composition.

In still another aspect, the present invention relates to a coatedsubstrate comprising a substrate together with a coating on saidsubstrate, said coating being produced by (a) contacting the substratewith a coating composition comprising the above-described antimicrobialcomposition, and (b) drying said coating composition on said substrateto produce said coated substrate.

In yet another aspect, the present invention relates to a paintcomprising:

(a) a base medium comprising water or a resin selected from the groupconsisting of vinyl, alkyd, epoxy, acrylic, polyurethane and polyesterresins, and combinations thereof, and

(b) the above-described antimicrobial composition. The antimicrobialcomposition is employed in the paint in an amount at least sufficient toact as an "in-can preservative" during storage prior to use.Alternatively, the antimicrobial composition can be employed in anamount sufficient to provide antimicrobial efficacy for the paint whendried on a substrate.

In still another aspect, the present invention relates to a soap,shampoo or skin care medicament comprising a suitable carrier and theabove-described antimicrobial composition.

In still another aspect, the present invention relates to a metalworkingfluid containing water or an organic base fluid, and the above-describedantimicrobial composition. Another aspect of the invention relates tothe above-described metalworking fluid which additionally comprises acomponent selected from the group consisting of corrosion inhibitors,surfactants, and combinations thereof.

In yet another aspect, the present invention relates to a compositioncomprising a plastic or a woven or non-woven fiber which comprises, incombination, a plastic or a fiber and the above-described antimicrobialcomposition.

These and other aspects will become apparent upon reading the followingdetailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It has now been surprisingly found in accordance with the presentinvention that the combination of pyrithione acid, or a salt thereof,with a select carboxylic acid, or salt thereof, with the benzyl andlower alkyl ester of para-hydroxybenzoic acid (also referred to hereinas "paraben"), or a salt thereof, or a combination thereof, providessynergistic antimicrobial effectiveness as an antifungal andantibacterial composition. An increased understanding of the mode ofaction in accordance with the present invention provides a betterunderstanding of antimicrobial enhancing additives for use incombination with pyrithione. Without wishing to be bound by anyparticular theory, it is believed by the present inventors that thesynergistic efficacy associated with the compositions of the presentinvention is attributable to the relative toxicity of the carboxylicacid or paraben co-biocide to the microorganism being attacked in thepresence of the pyrithione biocide in view of the present inventorsunderstanding of the antimicrobial mode of action of pyrithione. Thepyrithione acts to collapse the proton motive force that provides theenergy link for microbial metabolism, by catalyzing the electroneutralexchange of hydrogen ions and potassium ions across microbial cellmembranes.

In light of the above-described mode of action, the present inventorshave discovered that select classes of compounds provide synergisticantimicrobial effectiveness in combination with pyrithione, namelyspecific carboxylic acids, or salts thereof, or the benzyl and loweralkyl esters of para-hydroxybenzoatic acid (also referred to herein as"paraben"), or a salt thereof, or combinations of these compounds. Theterm "paraben" is also intended to encompass organic solutions, such asethanolic solutions of methylparaben ("MP"), propylparaben ("PP"), orbutylparaben ("BP").

As used herein, the term "synergistic antimicrobial effectiveness" meansthat the composition exhibits greater antimicrobial activity than theadditive amounts of activity provided when each component of thecombination is employed alone. The composition exhibits synergisticantimicrobial activity with respect to the growth of microorganisms,notably bacteria and fungi. The antimicrobial activity is providedduring use of the composition, for example, in an aqueous industrialfunctional fluid composition, such as a metalworking fluid, lubricant,or diagnostic reagent for immunological testing, in order to providebiocidal protection against microbes such as bacteria and fungi duringuse of the fluid.

The pyrithione used in the process and composition of this invention ispreferably a pyrithione salt, such as sodium pyrithione, zincpyrithione, chitosan pyrithione, magnesium disulfide pyrithione, copperpyrithione, and the like, although pyrithione acid can be used ifdesired. More preferable pyrithione salts include sodium pyrithione,copper pyrithione, and zinc pyrithione, most preferably sodiumpyrithione.

The sodium pyrithione useful in the present invention is a well-knowncommercial product that is commonly made by reacting2-chloropyridine-N-oxide with NaSH and NaOH, as illustrated by thedisclosures of U.S. Pat. No. 3,159,640.

Zinc pyrithione may be made by reacting 1-hydroxy-2-pyridinethione(i.e., pyrithione acid) or a soluble salt thereof with a zinc salt(e.g., ZnSO₄) to form a zinc pyrithione precipitate, as illustrated bythe disclosures of U.S. Pat. No. 2,809,971.

In use, the antimicrobial composition of the present inventionpreferably contains a weight ratio of carboxylic acid, or salt thereof,to pyrithione of between about 1:1 and about 10,000:1, more preferablybetween about 1:1 and about 6,000:1. If paraben or a salt thereof isemployed in the antimicrobial composition, then it is preferred that theweight ratio of the paraben compound to the pyrithione be between about1:10 and about 10,000:1, more preferably between 1:6 and 156:1.

The antimicrobial compositions of the present invention are suitable fora variety of uses, such as, for example in soap, shampoo, skin caremedicaments, metalworking fluids, paint, or incorporated into or ontoplastic or a woven or non-woven fibers.

One significant use application for the antimicrobial compositions ofthe present invention is in functional fluids, such as metalworkingfluids. These functional fluids are typically supplied as an aqueousconcentrate containing the antimicrobial composition and the othercomponents of the functional fluid. In the aqueous concentrate, asufficient amount of the antimicrobial composition is provided such thatthe "working" functional fluid will contain a biocidally effectiveamount thereof. In order to satisfy this requirement, the concentratefor a metalworking fluid, for example, preferably contains a totalamount of up to about 2.5 weight percent of the antimicrobialcomposition, based upon the weight of the metalworking fluid, in orderto provide a preferred amount of at least about 1250 ppm of theantimicrobial composition in the "working" fluid, based upon a dilutionrate of the concentrate to the "working" fluid of between about 1:10 andabout 1:100. Other functional fluids, such as cosmetics, are oftenformulated directly (without the need for a concentrate) and can containup to 5000 ppm, or more, of the antimicrobial composition.

The antimicrobial compositions of the present invention are also usefulin paints, including indoor and outdoor household paints, industrial andcommercial paints. Particularly advantageous results are obtained whenthe compositions of the present invention are utilized in conjunctionwith marine paints for use, for example, on ship's hulls. In addition,the antimicrobial compositions provide desirable results in exteriorpaints of the latex and alkyd types. The antimicrobial composition isalso useful as an "in-can" preservative during storage and prior to useof the paint.

Typically a paint composition will contain a resin, a pigment, andvarious optional additives such as thickening agent(s), wetting agentsand the like, as is well known in the art. The resin is preferablyselected from the group consisting of vinyl, alkyd, epoxy, acrylic,polyurethane and polyester resins, and combinations of thereof. Theresin is preferably employed in an amount of between about 20% and about80% based upon the weight of the paint or paint base.

In addition, the paint composition of the present invention optionallyadditionally contains optional additives which have a favorableinfluence on the viscosity, the wetting power and the dispersibility, aswell as on the stability to freezing and electrolytes and on the foamingproperties. If a marine paint is being fabricated, the paint preferablycontains a swelling agent to cause the paint to gradually "slough off"in its marine environment, thereby causing renewed biocidal efficacy ofnewly exposed biocide at the surface of the paint in contact with thewater medium of the marine environment. Illustrative swelling agents arenaturally occurring or synthetic clays, such as kaolin,montomorillonite, and bentonite), clay mica (muscovite), and chlorite(hectonite), and the like. In addition to clays other swelling agents,including natural or synthetic polymers, such as that commerciallyavailable as POLYMERGEL, have been found to be useful in thecompositions of the present invention to provide the desired "sloughingoff" effect. Swelling agents can be used singly or in combination. Thetotal amount of optional additives is preferably no greater than 20% byweight, more preferably between about 1% and about 5% by weight, basedupon the total weight of the paint composition.

Illustrative, thickening agents include cellulose 30 derivatives, forexample methyl, hydroxyethyl, hydroxypropyl and carboxymethyl cellulose,poly(vinyl alcohol), poly (vinylpyrolidone), poly(ethyleneglycol), saltsof poly(acrylic acid) and salts of acrylic acid/acrylamide copolymers.

Suitable wetting and dispersing agents include sodium polyphosphate,salts of low molecular weight poly(acrylic acid), salts of poly(ethanesulfonic acid), salts of poly (vinyl phosphonic acid), salts ofpoly(maleic acid) and salts of copolymers of maleic acid with ethylene,1 olefins 3 to 18 carbon atoms and/or styrene.

In order to increase the stability to freezing and electrolytes theremay be added to the paint composition various monomer 1.2-diols forexample glycol, propylene glycol (1.2) and butylene glycol 1.2) orpolymers thereof, or ethoxylated compounds. For example reactionproducts of ethylene oxide with long-chain alkanols, amines, alkydphenols, poly(propyleneglycol), or poly(butylene glycol), or acombination thereof, or the like.

The minimum temperature of film formation (white point) of the paintcomposition may be reduced by adding solvents, such as ethylene glycol,butyl glycol, ethyl glycol acetate, ethyl diglycol acetate, butyldiglycol acetate, benzene or alkylated aromatic hydrocarbons. Asdefoaming agents there are suitable for example poly(propylene glycol)and polysiloxanes. Optionally other biocides can additionally beincorporated into the paint formulations of the present invention.Useful optional solvents include methylisobutylketone (herein referredto as "MIBK"), xylene, ethyl benzene, methanol, and combinationsthereof.

The paint composition of the present invention may be used as a paintfor natural or synthetic materials, for example wood, paper, metals,textiles and plastics. It is particularly suitable as an outdoor paint,and is excellent for use as a marine paint.

The compositions of the present invention are useful, in any of thevariety of applications described herein, as disinfectants andpreservatives, in a liquid or spreadable solid form, alone or incombination with an inert carrier such as water, liquid hydrocarbons,ethanol, isopropanol, or the like. They can be employed usingconventional procedures to control bacteria and fungi in varioussubstrates, and can be applied to bacterial or fungal organisms or theirsubstrates in an antimicrobial amount by conventional procedures such asspraying, dipping, drenching impregnation, and the like.

The invention is further illustrated by the following Examples. Unlessotherwise stated, the "parts" and "%" are "parts by weight" and "percentby weight", respectively.

While the invention has been described above with references to specificembodiments thereof, it is apparent that many changes, modifications andvariations can be made without departing from the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents andother publications cited herein are incorporated by reference in theirentirety.

EXAMPLE 1 MIC Data on Pyrithione Plus Parabens or Carboxylic Acid

Interactions of sodium pyrithione with other compounds were assessedusing a modification of the "checkerboard" MIC ("minimum inhibitoryconcentration") procedure described by Dougherty, P. F., et al. 1977.Microdilution Transfer Plate Technique for Determining In Vitro Synergyof Antimicrobial Agents. Antimicrobial Agents and Chemotherapy.11:225-228. This procedure facilitates the measurement of the effects ofa large number mixtures of different ratios of biocides. Stock solutionsof pyrithiones in Tryptic Soy Broth (TSB) were diluted in TSB inmicroliter plates, and the test compounds were diluted in tubes of TSB.Aliquots of each dilution of test compound were added to the wellscontaining pyrithione dilutions and undosed TSB as a control, leavingrows of unmixed pyrithione or test compound for the determination ofMIC's of pure pyrithione or test compounds. An equal volume of testculture containing 10⁶ bacteria/ml or 10⁵ fungal spores/ml suspended inTSB was added to each well, and the plates were incubated at 28° C. Thelowest concentration resulting in growth inhibition (MIC) wasdetermined. The Fractional Inhibitory Concentration (FIC), ie. ratio ofthe MIC of a biocide in a mixture to that of the pure substance, wasdetermined, and the sum of the FIC's ("FIC Index") for each mixture wascalculated. Each type of interaction was quantified and categorizedaccording to the following: synergistic if <1; additive if =1;antagonistic if >1.

Mixtures containing varying proportions of pyrithione and organic acidsor methyl paraben synergistically inhibited a bacterium (Pseudomonasaeruginosa) and a fungus (Aspergillus niger), for which the MIC data aregiven in Tables 1 and 2, respectively.

                  TABLE 1                                                         ______________________________________                                        Synergistic Antibacterial Effects                                             of Sodium Pyrithione (NPT) Mixtures                                           MIC of Mixture (ppm).sup.a                                                                 Test                                                                          Compound  NPT,    Ratio   FIC                                    Test Compound                                                                              ("TC")    ppm     (TC/NPT)                                                                              Index.sup.b                            ______________________________________                                        none         0         128     --      --                                     salicylic acid                                                                             6250      0       --      --                                     "            3125      8       391/1   0.56                                   "            1563      32      49/1    0.50                                   "            781       32      24/1    0.38                                   "            391       64      6/1     0.56                                   p-aminobenzoic acid                                                                        6250      0       --      --                                     "            3125      16      195/1   0.63                                   "            1563      32      49/1    0.50                                   "            781       64      12/1    0.63                                   benzoic acid 6250      0       --      --                                     "            3125      4       781/1   0.53                                   "            1563      16      98/1    0.38                                   "            781       32      24/1    0.38                                   "            391       32      12/1    0.31                                   propionic acid                                                                             3125      0       --      --                                     "            1563      2       781/1   0.52                                   "            781       64      12/1    0.75                                   lactic acid  22,225    0       --      --                                     "            11,113    16      695/1   0.63                                   "            5560      32      174/1   0.50                                   "            2780      64      43/1    0.62                                   citric acid  >25,000   0       --      --                                     "            12,500    8       >1563/1 <0.56                                  "            6250      16      >391/1  <0.38                                  "            3125      16      >195/1  <0.25                                  "            1563      32      >49/1   <0.31                                  "            781       64      >12/1   <0.53                                  "            391       64      >6/1    <0.52                                  methyl ester of p-                                                                         2500      0       --      --                                     hydroxybenzoate                                                               methyl ester of p-                                                                         625       16      39/1    0.38                                   hydroxybenzoate                                                               methyl ester of p-                                                                         313       32      10/1    0.38                                   hydroxybenzoate                                                               methyl ester of p-                                                                         156       32      5/1     0.31                                   hydroxybenzoate                                                               methyl ester of p-                                                                         78        32      2/1     0.28                                   hydroxybenzoate                                                               methyl ester of p-                                                                         39        64      1/2     0.52                                   hydroxybenzoate                                                               methyl ester of p-                                                                         20        64      1/3     0.51                                   hydroxybenzoate                                                               methyl ester of p-                                                                         10        64      1/6     0.50                                   hydroxybenzoate                                                               none         0         64      --      --                                     sorbic acid  4096      0       --      --                                     "            2048      16      128/1   0.75                                   "            1024      32      32/1    0.75                                   "            512       32      16/1    0.63                                   "            256       32      8/1     0.56                                   ______________________________________                                         .sup.a Minimum Inhibitory Concentrations (MIC's) were determined against      Pseudomonas aeruginosa NCIMB strain 6749. NPT and inocula of bacterial        cells were added to Tryptic Soy Broth (TSB) adjusted to pH 5.8. Test          compounds were dissolved in TSB, and the resulting solutions were adjuste     to pH 5.8 and filtersterilized. The mixtures were diluted in TSB (pH 5.8)     and incubated at 28° C. for 4 to 6 days.                               .sup.b Fractional Inhibitory Concentration Index: additive effect if = 1;     synergistic if <1; antagonistic if >1.                                   

                  TABLE 2                                                         ______________________________________                                        Synergistic Antifungal Effects                                                of Sodium Pyrithione (NPT) Mixtures                                           MIC of Mixture (ppm).sup.a                                                                 Test                                                                          Compound  NPT,    Ratio   FIC                                    Test Compound                                                                              ("TC")    ppm     (TC/NPT)                                                                              Index.sup.b                            ______________________________________                                        none         0         32      --      --                                     salicylic acid                                                                             6250      0       --      --                                     "            3125      1       3125/1  0.53                                   "            1563      16      98/1    0.75                                   sorbic acid  1250      0       --      --                                     "            625       8       78/1    0.75                                   "            313       8       39/1    0.50                                   benzoic acid 1500      0       --      --                                     "            750       4       188/1   0.75                                   propionic acid                                                                             3125      0       --      --                                     "            1563      0.25    6252/1  0.51                                   "            781       4       195/1   0.38                                   none         0         64      --      --                                     methyl ester of p-                                                                         1250      0       --      --                                     hydroxybenzoate                                                               methyl ester of p-                                                                         625       4       156/1   0.56                                   hydroxybenzoate                                                               methyl ester of p-                                                                         313       16      20/1    0.50                                   hydroxybenzoate                                                               methyl ester of p-                                                                         156       16      10/1    0.38                                   hydroxybenzoate                                                               methyl ester of p-                                                                         78        16      5/1     0.31                                   hydroxybenzoate                                                               methyl ester of p-                                                                         39        16      2/1     0.28                                   hydroxybenzoate                                                               methyl ester of p-                                                                         20        32      1/2     0.52                                   hydroxybenzoate                                                               methyl ester of p-                                                                         10        32      1/3     0.50                                   hydroxybenzoate                                                               ______________________________________                                         .sup.a Minimum Inhibitory Concentrations (MIC's) were determined against      an environmental isolate of the fungus, Aspergillus niger. NPT and inocul     of fungal spores were added to Tryptic Soy Broth (TSB) adjusted to pH 4.5     Test compounds were dissolved in TSB, and the resulting solutions were        adjusted to pH 4.5 and filter sterilized. The mixtures were diluted in TS     (pH 4.5) and incubated at 28° C. for 12 to 13 days.                    .sup.b Fractional Inhibitory Concentration Index: additive effect if = 1;     synergistic if <1; antagonistic if >1.                                   

EXAMPLE 2 Metalworking Fluid Containing Pyrithione and Paraben

The efficacy of a sodium pyrithione-methyl paraben mixture as apreservative was measured in an oil in water emulsion metalworking fluidchallenged with a mixture of bacteria and fungi. A 5% aqueous emulsionof concentrated MWF, consisting of mineral oil (83.5%), sulfonatedhydrocarbon (10.7%), oleic acid (1.0%), triethanolamine (0.8%), methyltallowate (3.0%), and propylene glycol ether (1.0%) was dosed with 125ppm of sodium pyrithione and 1000 ppm of methyl paraben and dispersedinto Erlenmeyer flasks. A challenge level of 10⁷ cells of bacteria and10⁵ fungal spores per ml of emulsion was initiated by adding asuspension of seven bacteria and two fungi originally isolated fromcontaminated MWF's (Pseudomonas rubescens NCIMB 12202, Pseudomonasstutzeri sp., Pseudomonas fluorescens NCIMB 12201, Pseudomonasaeruginosa NCIMB 6749, Pseudomonas oleovorans NCIMB 6576, Alcaligenesfaecalis sp., Citrobacter freundii NCIMB 12203, Fusarium sp. andCephalosporium sp.). The fluids were agitated continuously on a rotaryshaker and sampled periodically for viable bacteria on Tryptic Soy Agarand for fungi on Tryptic Soy Agar supplemented with 100 mg gentamicinsulfate per liter. After two weeks, a pronounced synergistic inhibitionof bacteria and fungi was observed in the pyrithione-methyl parabenfluid relative to the untreated control, as shown by the data presentedin Table 3 below. Inhibition was also established when the fluids werechallenged a second time (see Table 3).

                  TABLE 3                                                         ______________________________________                                        Efficacy of Sodium Pyrithione/Methyl Paraben                                  Mixture in an Oil in Water Emulsion*                                                       Time   Average Viable Count/ml                                   Treatment      (days)   Bacteria   Fungi                                      ______________________________________                                        blank          7        20,700,000 150,000                                    NPT (125 ppm)  7        12,400,000 134,000                                    MP (1,000 ppm) 7        5,930,000  44,000                                     NPT (125) + MP (1000)                                                                        7        >1,000,000 27,000                                     blank          12       25,900,000 94,000                                     NPT (125 ppm)  12       8,190,000  44,000                                     MP (1,000 ppm) 12       442,000    53,000                                     NPT (125) + MP (1000)                                                                        12       <260       100                                                     14     Re-challenge                                              blank          19       39,500,000 152,000                                    NPT (125 ppm)  19       25,200,000 106,000                                    MP (1000 ppm)  19       4,160,000  74,000                                     NPT (125) + MP (1000)                                                                        19       25,700     19,200                                     blank          27       29,500,000 270,000                                    NPT (125 ppm)  27       16,500,000 50,000                                     MP (1000 ppm)  27       375,000    50,000                                     NPT (125) + MP (1000)                                                                        27       <26,000    <1000                                      ______________________________________                                         *5% aqueous emulsion of metalworking fluid concentrate treated with sodiu     pyrithione (NPT) and methyl paraben (MP).                                

EXAMPLE 3 Latex Paint Containing Sodium Pyrithione and Paraben

The efficacy of sodium pyrithione plus paraben mixtures was measured ina latex paint artificially contaminated with Pseudomonas aeruginosa. Arepresentative vinylacrylic flat latex house paint formulation(consisting of water (30%), ethylene glycol (2.20%), anionic dispersant(0.58%), defoamer (0.33%), hydroxyethyl cellulose (0.25%), potassiumtripolyphosphate (0.08%), silicate filler (20.60%), titanium dioxide(18.50%), propylene glycol (2.80%), attapulgite clay (0.49%), alcoholethoxylate (0.21%), latex (30.20%), and an alcohol ester coalescent(0.74%)) was diluted in sterile water to 10% to simulate a factory rinsewater-condensation situation and inoculated with a broth culture ofPseudomonas aeruginosa ATCC 10145. Growth was monitored by culturing thepaint solution on slants of Tryptone Glucose Extract Agar (TGEA, Difco)incubated at 29° C. for 5 days. Ten grams of uncontaminated 10% paintwere weighed into glass vials and amended with aqueous solutions ofsodium pyrithione (referred to herein as "SP") or ethanolic solutions ofmethylparaben ("MP"), propylparaben ("PP"), or butylparaben ("BP").Blanks containing an equivalent amount of ethanol (50 microliters) wereincluded. Each vial was inoculated with 1% by volume of contaminateddilute paint (2.0×10⁶ CFU/ml). Survival of the contaminant was assessedperiodically by subculturing the samples to slants of TGEA as before.After 32 days, the paint samples were re-challenged with 1% by volume ofthe dilute contaminated paint.

The results provided in Table 4 show that mixtures of 500 ppm ofpyrithione and 1000 ppm of paraben were more antimicrobially effectiveafter one week than either preservative alone. In addition the data inTable 4 indicate that methyl- and propylparabens were relatively moreeffective synergists than butylparaben. After re-challenge, acombination of 1000 ppm methylparaben and between 500 and 1000 ppmsodium pyrithione was the most effective synergistic combination in thistest.

In a second experiment, for which the results are shown in Table 5,undiluted similarly contaminated paint was amended with methylparabenand sodium pyrithione in various ratios and periodically assayed forgrowth as in the first experiment. The samples were rechallenged with 2%by volume of contaminated paint (8.7×10⁶ CFU/ml) on the 21st and 69thdays. Mixtures of 500 pppm sodium pyrithione plus 500 or 1000 ppmmethylparaben proved to be effective throughout much of the test, but500 ppm sodium pyrithione plus 1000 ppm methylparaben provided maximumantimicrobial effectiveness in this test. The results are given in Table5.

In Tables 4 and 5 "-" denotes no surviving microbial growth of the testorganism, whereas "+" denotes very little survival, "++ and +++" denoteminimal microbial survival, and "++++" and "+++++" denote significantmicrobial survival.

                                      TABLE 4                                     __________________________________________________________________________    IN-CAN PAINT PRESERVATIVE EFFICACY                                                 GROWTH (TGEA Subculture)                                                 DAY  Preservative (ppm, w/w)                                                  __________________________________________________________________________         blank  SP 500 SP 1000                                                                              MP 1000                                                                              PP 1000                                                                              BP 1000                               __________________________________________________________________________    1    +++++  ++++   +++    +++++  +++++  +++++                                 8    +++++  +++    ++     +++++  +++++  +++++                                 15   +++++  ++++   +      +++++  +++++  +++++                                 25   +++++  +++++  -      +++++  +++++  +++++                                 32   Re-challenge                                                             39   +++++  +++++  +++    +++++  +++++  +++++                                 __________________________________________________________________________         SP     SP     SP     SP     SP     SP                                         500 + MP                                                                             500 + PP                                                                             500 + BP                                                                             1000 + MP                                                                            1000 + PP                                                                            1000 + BP                             __________________________________________________________________________    1    ++++   ++++   ++++   +++    ++++   ++++                                  8    +      ++     +++    +      ++     ++                                    15   -      -      ++     -      -      +                                     25   -      -      +      -      -      -                                     32   Re-challenge                                                             39   ++     ++++   ++++   +      +++    +++                                                      +                                                          __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    EFFICACY OF PYRITHIONE + METHYLPARABEN MIXTURES                               GROWTH (TGEA Subculture)                                                      Preservatives (ppm, w/w)                                                                                         SP 250 SP 500 SP 250 SP 500                           SP    SP    MP    MP    ppm +  ppm +  ppm +  ppm +                 DAY  blank 250 ppm                                                                             500 ppm                                                                             500 ppm                                                                             1000 ppm                                                                            MP 500 ppm                                                                           MP 500 ppm                                                                           MP 1000                                                                              MP 1000               __________________________________________________________________________                                                            ppm                   7    +++++ +     +     +++++ +++++ ++++   ++     +++    +                     14   +++++ -     -     +++++ +++++ -      -      -      -                     21   +++++ -     -     +++++ +++++ -      -      -      -                     Re-challenge                                                                  28   +++++ +++++ -     +++++ +++++ ++     +      +      -                     35   +++++ +++++ -     +++++ +++++ -      -      -      -                     42   +++++ +++++ -     +++++ +++++ +      -      -      -                     49   +++++ +++++ -     +++++ +++++ +++    -      -      -                     56   +++++ +++++ -     +++++ +++++ -      -      -      -                     63   +++++ +++++ -     +++++ +++++ +/-    -      -      -                     69   +++++ +++++ -     +++++ +++++ +/-    -      -      -                     Re-challenge                                                                  72   +++++ +++++ ++++  +++++ +++++ +++++  +      +++    -                     79   +++++ +++++ +++++ +++++ +++++ +++++  ++++   +++++  -                     __________________________________________________________________________

What is claimed is:
 1. An antimicrobial composition characterized bysynergistic antibacterial and antifungal efficacy and comprisingpyrithione acid or a pyrithione salt, or a combination thereof, and atleast one compound selected from the group consisting of benzyl andlower alkyl esters of para-hydroxybenzoic acid, salts thereof, andcombinations thereof.
 2. The composition of claim 1 wherein saidcompound is a benzyl or lower alkyl ester of para-hydroxybenzoic acid,or a salt thereof, and the weight ratio of said compound to saidpyrithione salt or pyrithione acid is between about 1:10 and about10,000:1.
 3. A method of imparting antimicrobial activity to acomposition comprising water or an organic solvent which comprisesadding thereto an antimicrobially effective amount of pyrithione acid ora pyrithione salt, or a combination thereof, and at least one compoundselected from the group consisting of benzyl and lower alkyl esters ofpara-hydroxybenzoic acid, salts thereof, and combinations thereof. 4.The method of claim 3 wherein said compound is a benzyl or lower alkylester of para-hydroxybenzoic acid, or a salt thereof, and the weightratio of said compound to said pyrithione salt is between about 1:1 andabout 6,000:1.
 5. A method of coating a substrate to provide anantimicrobially effective coating on the substrate which comprisescontacting the substrate with a coating composition comprisingpyrithione acid or a pyrithione salt, or a combination thereof, and atleast one compound selected from the group consisting of benzyl andlower alkyl esters of para-hydroxybenzoic acid, salts thereof, andcombinations thereof.
 6. The method of claim 5 wherein said compound isa benzyl or lower alkyl ester of para-hydroxybenzoic acid, or a saltthereof, and the weight ratio of said compound to said pyrithione saltis between about 1:1 and about 6,000:1.
 7. A coated substrate comprisinga substrate together with a coating on said substrate, said coatingbeing produced by:(a) contacting the substrate with a coatingcomposition comprising pyrthione acid or a pyrithione salt, or acombination thereof, and at least one compound selected from the groupconsisting of benzyl and lower alkyl esters of para-hydroxybenzoic acid,salts thereof, and combinations thereof, to provide a coating on saidsubstrate, and (b) drying said coating composition on said substrate toproduce said coated substrate.
 8. The coated substrate of claim 7wherein said compound is a benzyl or lower alkyl ester ofpara-hydroxybenzoic acid, or a salt thereof, and the weight ratio ofsaid compound to said pyrithione salt is between about 1:1 and about6,000:1.
 9. A paint comprising:(a) a base medium comprising water or aresin selected from the group consisting of vinyl, alkyd, epoxy,acrylic, polyurethane and polyester resins, and combinations thereof,(b) pyrithione acid or a pyrithione salt, or a combination thereof, and(c) a compound selected from the group consisting of benzyl and loweralkyl esters of para-hydroxybenzoic acid, salts thereof, andcombinations thereof.
 10. A soap, shampoo or skin care medicamentcomprising a suitable carrier, pyrithione acid or a pyrithione salt, ora combination thereof, and a compound selected from the group consistingof benzyl and lower alkyl esters of para-hydroxybenzoic acid, saltsthereof, and combinations thereof.
 11. A metalworking fluid containingwater or an organic base fluid, a pyrithione, and a compound selectedfrom the group consisting of benzyl and lower alkyl esters ofpara-hydroxybenzoic acid, salts thereof, and combinations thereof. 12.The metalworking fluid of claim 11 which additionally contains acomponent selected from the group consisting of corrosion inhibitors,surfactants, and combinations thereof.
 13. A composition comprising aplastic or a woven or non-woven fiber which comprises, in combination, aplastic or a fiber and a compound selected from the group consisting ofbenzyl and lower alkyl esters of para-hydroxybenzoic acid, saltsthereof, and combinations thereof.